1. Field of the Invention
The present invention relates to an air flow measurement device and air flow correction method for correcting an air flow amount based on temperature and flow amount.
2. Description of the Related Art
In a vehicle engine, methods for controlling the amount of fuel supply to the engine as a function of an intake air flow amount are generally known, as are air flow measurement devices provided in an intake pipe of an engine.
A typical air flow measurement device includes a flow sensor. However, because of measurement variations in each flow sensor, the air flow measurement device must either calibrated before shipment or correct the measurement variation of the flow sensor and output the corrected value of the measurement variation to a control portion such as an ECU of the vehicle. For example, JP-A-11-183220, which corresponds to U.S. Pat. No. 6,321,165, describes an air flow measurement device that corrects a measurement value of a hot wire type flow sensor configured with a temperature-responsive heating resistor and outputs the corrected value.
In a typical hot-wire flow sensor, a measurement value, such as a voltage value, for a given flow amount changes depending on the intake air temperature. Specifically, as shown in FIG. 5, for a flow amount of G1, the output voltage for an intake air temperature of 130° C. is VD3, while the output voltage for the flow amount G1 at an intake air temperature of 20° C. is VD4. A temperature characteristic between the flow amount and the measurement value, such as the output voltage, can be established as shown in FIG. 5.
However, in a typical hot-wire sensor system, such as that described in JP-A-11-183220, the temperature characteristic is not taken into account when the corrected measurement value is output to the engine control portion. In the case where the relationship, for example between the output voltage value and the temperature, is the same for each flow amount measurement, the ratio of correction of, for example, voltage VD 1 to voltage VD2 or voltage VD3 to voltage VD4 as shown in FIG. 5, which can be referred to as a correction coefficient, is the same. However, the relationship between the output voltage value and the temperature based on the flow amount changes for each different flow amount. In such a case, the correction coefficient may depend on the flow amount, and the temperature correction coefficient cannot be determined based on information from only the intake air temperature.